The present invention relates generally to record disc cutting styluses and more particularly to a stylus for cutting and recording multichannel signals on a record disc.
A 4-channel record disc recording system is disclosed in U.S. Pat. Nos. 3,686,471 and 3,883,699. In this system, the signals of pairs of channels are matrixed to obtain respective sum and difference signals. Then, after a carrier wave of 30 KHz, for example, is angle modulated with a difference signal, the resulting angle-modulated difference signal of a band of 20 KHz to 45 KHz is multiplexed with a direct wave sum signal of a band of 30 Hz to 15 KHz. The signal thus multiplexed is cut and recorded on a record disc.
The sound groove of a record disc, which has a been cut in this manner has waveform resulting from the superimposition of a small amplitude angle-modulated difference signal of relatively high frequency on a large amplitude direct wave sum signal of relatively low frequency.
In the recording system of a conventional 2-channel stereo record disc, it is necessary merely to cut and record direct wave signals of the audio-frequency band. For this reason, any distortion in the conventional groove waveform is not perceived to any great degree by the auditory sensing of the reproduced sound. However, this nonperception is not true for a multichannel record disc on which a multiplexed signal of a direct wave signal and an angle-modulated signal is recorded. If there is a distortion in the groove waveform of the direct wave signal, there is a high-frequency component of the direct wave signal due to this distortion which becomes admixed within the band of the angle-modulated wave. Then there is an aggravation of cross-talk and noise. Furthermore, this distortion in the groove waveform of the direct wave signal shifts the phase of the angle-modulated wave signal that is recorded in a superimposed state relative to the direct wave signal. Undesired phenomena occur when the angle-modulated wave signal is reproduced.
There is a distortion when a signal is cut and recorded on a record disc by means of a conventional cutting stylus. The waveform of the groove has a considerable distortion due to the shape of the cutting stylus as will be described hereinafter with reference to the drawings. In a 2-channel stereo record disc, only direct wave signals are recorded and the distortion does not become a problem to the auditory sense. For this reason, little consideration has heretofore been given to the shape of the cutting stylus with respect to distortion. Consequently, when a multiplexed multichannel signal is cut and recorded with a conventional cutting stylus, the distortion gives rise to an impaired frequency characteristic and a cross-talk characteristic.